Method for the production of screen negatives



June 11, 1940.

Filed June 24, 1938 4 Sheets-Sheet 1 Wbau JQ QL Q 3 mm 5 m3 3 M3. Q N

1N VENTORS MM 5 MW #m 5 T Y wp 5 H ATTORNEYS June 11, 1940. Q HANSCH ET AL 2,204,080

METHOD FOR THE PRODUCTION OF SCREEN NEGATIVES Filed June 24, 1938 4 Sheets-Sheet 4 ATTORNEY 3 Patented finite ill, 394$ UNETEfi S'E ATES ascents METHOD FOR THE PRODUCTION 6F SCREEN NEGATIVES August 0. Piansch and Henry E. Hanson,

. Whippany, lilo ,3,

Application june 2 1 193$, Serial No. 215,55@

5 Claims.

nation intensity upon the surface of the original and the sensitivity of the film.

Heretofore in the production of screen negatives, the duration of exposure or the interval of light action upon the sensitive film has depended largely upon the experience and skill of the operator and when confronted with an unusual original or a peculiar requirement, the procedure has been by trial and error with obvious uncertain results.

The practice now in vogue for exposing screen negatives has been evolved from the art of general photography but if scientific controlof exposure of screen negatives is to be substituted for rule of thumb, such methods become inefficient. Aside from a few rules for calculating screen separation and lens stops, the art has heretofore left the craftsman on his own resources. With these rules as a basis, some craftsmen irrespective of screen pitch employ one series of stops for each camera extension and attempt a surmise of the tonal quality of the original varying the exposure in accordance with their judgment. Others determine the screen separation in accordance with Lord Rayleighs pin-hole formula which requires for every magnification ratio a different series of stops for each screen pitch with a change in the exposure intervals and as a consequence thereof disregard other essential factors.

The various factors entering into the exposure, together with certain extraneous conditions, some, of which may at times be unstable in their actions, have heretofore been deemed unsurmountable obstacles and thereby acted as a di'srrent to any serious attempt to arrive at a complete method for determining the correct composite interval of light action.

In order to devise a method which obviates the uncertain element of personal skill, a systematic consideration of the relative effects of all of the factors is required as any advantage gained by the control of one factor becomes effective only if all other factors are controlled with accuracy.

The invention, therefore, embodies a method which includes stepsand formulas for establishing the emissive light energy of several tones of the original due to the reflection density thereof and the illumination intensity thereon and fur= ther includes the determination of certain inter vals of space as applied to camera extension, stop openings and screen separation and the application thereof, which together with the size of the screen apertures cause restrictions and modifications of the light wave energy so that at the picture plane the impressive energy of the light action results in images displaying uniformly long tonal ranges.

The invention is directed to a method of pro ducing screened negatives which comprehends a consideration and computation of every essential factor which affects the light action then cor relating the computation of said factors in order. to obtain a definite time for the interval of exposure for each stop opening employed.

When excessive refinishing or reetching becomes necessary, the tone gradations present in the original become replaced by harsh or unnatural brush marks which are objectionable, therefore it is necessary to retain the delicate shadings in the negative which are visible in the original. It is, therefore, an object of the present invention to provide a method whereby screen negatives will possess a tonal range which will minimize or eliminate the amount of refinishing or reetching necessary.

More particularly the invention resides in a method of obtaining intervals of exposure by establishing magnification ratio, camera extension,

-' pitch of the screen and size of the screenapertures, determining screen separation, diameters of the several stop openings employed, compensating for required stop opening sizes between available stop opening sizes, ascertaining the tonal range of the original, the light intensity upon the surface of the original and the sensitivity of each batch of film employed and then employing the said results so established or determinedin the exposure of a screen negative.

With the aforementioned and other objects in view, the invention is set forth in greater detail in the following specification and illustrated in the accompanying drawings.

In the drawings:

Fig. 1 is a reference table embodying certain of the factors established in accordance with the method.

Fig, 2 is a table listing and identifying the sizes of available or standard stop openings and their corresponding F values.

Fig. 3 is a table listing and identifying the various series of available or standard stop openings.

Fig. 4 is a tonal wedge for ascertaining the tonal range of originals and negatives.

Fig. 5 is a refiection value chart complementary to the tonal wedge.

Fig. 6 is a table of exposure intervals for various tonal ranges.

Fig. 7 is a perspective view illustrating an original arranged in a copy-holder with the means employed for determining the light intensity on the surface of the original.

Fig. 8 is an enlarged face view of the photo-cell illustrating the adjustable mask.

Light waves from an illuminated original after passing through an objective form an image at a certain plane and the impressive energy of this light action upon a light sensitive film will produce a negative after development. By interposing a cross line screen in the path of the light waves, additional factors enter into the intervals of exposure which do not exist in general photography. Illumination 'intensity and reflection density determine the emissive energy for each tone inherent in an original and the distance between the original and the lens establishes the loss of energy at the surface of the lens. A stop opening imposes a definite restriction to the light waves passing through the lens while the screen apertures and separation further obstruct and modify the impressive effect of the light motion so that at the picture plane the impressive force is proportional to the aforementioned factors and the camera extension.

In order to produce screened negatives which will consistently approximate the fidelity possible by continuous tone renderings, necessitates the establishment of standards for the effective light energy and the subsequent conversion of these standards into intervals of light action so that the aperture patterns composing the image will be of proper size and form.

The size of a screened negative to be produced from an original is given. by the requirements of the customer and the proportion existing between the original and negative is hereinafter referred to as the magnification ratio.

The magnification ratio is determined in the usual manner which is as follows: The larger dimension becomes the divisor and the smaller the dividend regardless of whether these dimensions apply to the original or reproduction and the quotient thereof is the magnification ratio.

When the negative is to be larger than the original, a capital letter E is affixed before the percentage thus indicating an enlargement, otherwise the ratio expresses reduction.

In carrying out the method, after having ascertained the magnification ratio and knowing the focal length of the lens being used, the following formulas determine the camera extension: One plus magnification ratio multiplied by focal length of lens equals camera extension for reductions. For instance, if the focal length of the lens is 18" and the magnification ratio 50%, this equation is expressed as follows:

1 plus .50 times 18=camera extension for reductions. Hence the result will show a camera extension of 27".

One and one divided by magnification ratio, then multiplied by focal length of lens equals camera extension for enlargements. For instance, if the focal length of the lens is 18" and the magnification ratio is E50%, the equation is expressed as follows:

1 p 1 u camera extension for 1:.50 tunes l8 enlargements Hence, the result will show a camera extension of The given screen pitch establishes the width of the apertures of the screen to be employed.

The screen separation or distance between the screen ruling and the sensitive film is then ascertained by the following formula: In which the square of the width of the aperture of the screen is the dividend, pi multiplied by the wave 7 length of light causing the predominant action on the sensitive film is the divisor, and the screen separation is the quotient, the equation is thus expressed as follows:

Width of screen aperture 2 in inches Screen Pi times wave length of light in inches aration 3.14 times .00OOl6 A simpler formula which yields similar results is as follows: Screen separation is the quotient which is arrived at by employing the width of the screen aperture, multiplied by the fourthpower of ten as the dividend, and the screen pitch as the divisor. Utilizing this formula the separation for a screen ruled one hundred lines to the linear inch is expressed by the following equation:

.005 times 1o* o 100 100 Having established the camera extension, width of the screen aperture and screen separation, the diameter of the detail stop opening is then determined in accordance with the following formula: Wherein the width of the screen aperture multiplied by the camera extension is the dividend, the screen separation the divisor and the quotient the diameter of the detail stop opening. For example, using a one hundred pitch screen having a screen aperture of .005 at a required camera extension of 36", with a screen separation of .5", the diameter of the detail stop opening will be found to be .36

.005 tsimes 36 To properly balance the screen image, the area of the middletone stop opening'should be twice the area of the detail stop opening and one-half the area of the highlight stop opening. In order to obtain the proper areas of the middletone and highlight stop openings, the diameters which will produce such areas may be ascertained by the following formulas: Diameter of highlight stop opening is the diameter of detail stop opening multiplied by two. Diameter of middletone stop opening shall be the square root of the sum of the diameter of detail stop opening squared and the diameter of highlight stop open ing squared. For example, with a detail stop opening having a diameter of .36", the diameter of the highlight stop opening becomes .36 times 2 or .72". The equation for arriving at m middletone stop is expressed as follows When the screen separation and the diameters of the stop openings have been determined in accordance with the foregoing formulas, the exposure intervals for each screen remain constant for all magnification ratios provided the other factors remain unchanged. It, therefore, becomes possible to establish an exposure ratio for each screen employed.

Inasmuch as the screen ruled with 133 lines to the inch is the most commonly used for commercial reproduction, this screen pitch will be herein considered as the standard and adopted as unity for these calculations. The formula for determining the time ratio for any other screen having equi-distant ruling is as follows: The square of the diameter of the detail stop opening required for the standard or 133v screen, at a magnification ratio of one divided by the square of the diameter of the detail stop opening for a new screen at the same camera extension equals the time interval for the new screen. This may be expressed in the following equation:

Diameter of detail stop for standard screen I Diameter of detail stop for new screen 1 time interval for new screen or For example, if the diameter of the detail stop at unity magnification ratio for the standard screen is .5" and the diameter of the detail stop for the screen ruledwith one hundred lines to the inch is .38", the time'interval for the new screen becomes 1.68.

While precision in exposure control demands many sized stop openings, convenience in operation dictates a conservative limit to the number thereof. By employing the third root of 1.414 which is 1.0904 as a basis for calculating the different stop openings, forty different standard sized stop openings are established between stop openings F8 and F235 inclusive, as illustrated in Fig. 2 of the drawings. I

The stop openings in accordance with their F value are progressively numbered from one to forty and alongside each F value the diameter of the stop opening for a lens having a focal length of 18" is given in inches or decimals thereof, F value 8 being assigned number 1 and F value 235, number 40. The numbers assigned to the F values are employed as key numbers in the chart illustrated in Fig. 3 to designate the various availableor standard stop openings which are .one to twenty-five.

in Fig. 2, the key numbersof'the stop openings I may be utilized to ascertain the diameters in inches or decimals thereof. For example, series three" has grouped thereunder key number'24 for the highlight stop opening, key number 28 for the middletone stop openingand key number 32 for the detail stop opening. By reference to the chart in Fig. 2 the keynumber 24 shows an, F value of 58.7 and a diameter of .28" for the' highlight stop, the key number 28 shows an F value of 83 and a diameter of .197" for the middletone stop opening and the key number 32 shows an F value. of 118 and a diameter of .139"

for the detail stop opening. These forty different standard stop openings will, therefore, vary at a ratio equal tothe square of 1.0904 which equals 1.189. While an apreciable difference will existbetween the diameters in any two stops, in the smaller sizes this difference will vary in thousandths of an inch. Whenever the diameters ofthe available standard stop openings .willnot agree with the calculated sizes for the camera extensionand required screen, a variation from the time ratio for said screen becomes necessary. This is established by the following formula:, X

Time variation for required camera extension or (Required camera extension) I (Camera extension where available standard stops agree with calculated stops) In carrying out the method, use is made of a reference table illustrated in Fig. 1 of the drawings, which table is ruled to provide vertical columns and horizontal rows, column l0 at the left of the table being designated by the heading "Screen pitch having indicated in the horizontal rows thereof the standard ruled screens which'indicate the number-of ruled lines to the inch. The next adjacent column II is headed Screen separation and. contains rows which indicate in units and decimal fractions the separation between the sensitive film and the actual ruling of the screen, the screen separation in each row corresponding respectively to thescreen pitch occurring in the same row. The vertical columns I2 between column H and column ii are provided with heading numerals indicating 'certainmagnification ratios between reductions cate the required series of stop openings given in the table in Fig. 3 for each particular screen at a certain magnification ratio.

A difference of 25% exists in the area of any two adjacent available stop. openings which difference, if not compensated for, would result in an exposure error of approximately 12%. This difference is conveniently divided into four parts each of which expresses a difference of 6%% so as to thereby minimize the greatest possible error to approximately 3% which is negligible. In the.

horizontal rows 15 in the table illustrated in Fig. 1 of the drawings, the letters B, C and D designatev the'inbetween stop variations between any two adjacent series of available stop openings.

Since the various series. of available stop openings are considered'as standard, the letter B for its respective magnification ratios designates an inbetween value or 106%% of the previous available stop opening series in the same row.

This value then becomes J in the formulas on this page and page 5 hereof.-

Likewise the letter C for its respective magnification ratios' designates ,an inbetween ,v'ahie orv 112 of the previous available stop opening series in the samerow which-becomes the value-for the letter J, and the letter I) for its respective magnification ratios designates an inbetween value or .118%% of the previous available stop" opening 1 series in said row and which likewise becomes the value for the letter J.

The method further consists in the determination of the tonal range of the original by means of which it is possible to establish the time intervals of light action for each of the tonal zones of the original. The visible reflection density of any portion of the original is herein termed a tone, the difference in reflection density between the lightest and darkest tones of an original is herein termed the tonal range and the number of tones inherent in an original or negative is herein termed the tonal scale.

It is necessary to determine the tonal range of the original in order that this information may be utilized in the determination of the various intervals for the composite exposure and thereby produce negatives having similar tonal range. For determining the tonal range of the original, standard tonal wedges are utilized one of which is shown in Fig. 4 and which consists of a strip of material, preferably transparent,

,havin'g twelve density reflection values varying from crystal clear or pure white, to the darkest tone which may be black or some color such as red, yellow, blue, sepia-brown or olive green. Each tone of the wedge is provided with identifying indicia, such as numbers, ranging from one to twelve, the lightest tone bearing indicia one and the darkest bearing indicia twelve.

To ascertain the tonal range of an original, a standard tonal wedge is placed over or adjacent to the apparent lightest area of the original and the wedge is then shifted until a tone of the wedge coincides with the reflection density of the area being checked, the number of the coinciding Wedge tone being then noted. A similar operation establishes the tone number for the darkest tone of the original and this number is also noted. These numbers represent the tonal range of the original.

Having noted these numbers, the detail exposure interval, middletone exposure interval and highlight exposure interval are then ascertained by reference to a chart and table, illustrated in Figs. 5 and 6 of the drawings. Thus, if the number of the tonal wedge for the lightest area is one and the number of the tonal wedge for the darkest area is twelve, the tonal range of the original is one to twelve. The tonal range determines the exposures for the various stop openings, thus one original with its darkest tone absorbing twice the amount of light as the darkest tone of another original, will require double the exposure time with the detail stop if both negatives shall be comparable. Likewise, the brightest tone of the first original reflecting twenty percent less light than the corresponding tone of the second original, will require a twenty percent longer exposure with the highlight stop in order to attain a similar highlight dot.

The complementary chart and table, illustrated in Figs. 5 and 6 of the drawings, giving calculated reflection values and exposure intervals of the tonal ranges of originals, are employed as a medium for classifying and readily distinguishing the intervals of exposure. The chart illustrated in Fig. 5, which is complementary to the tonal wedge, is divided into twelve columns which correspond in number and indicia with the tones of the tonal wedge. Inasmuch as the first tone or tone one of the wedge causes maximum reflection, the first column of the chart represents maximum reflection density and has been assigned the reflection density value of one hundred. Each succeeding tone oi. the wedge having approximately eight percent less reflection density, the relevant columns of the chart are desi nated by the corresponding percentages namely, ninety-two, eighty-four, seventy-six, sixty-eight, sixty, flfty-two, forty-four, thirty-six, twentyeight, twenty and twelve, the last division of the chart representing the darkest tone of the wedge being assigned the reflection density value of twelve percent.

The divisions of the chart are grouped into three overlapping zones, namely, highlight zone, middltone zone and detail zone, the highlight zone extending from column one to column five, inclusive, corresponding to the tones one to five of the tonal wedge; the middletone zone extending from column four to column nine, inclusive, and corresponding to tones four to nine of the tonal wedge, and the detail zone extending from column eight to column twelve, inclusive, and corresponding to tones eight to twelve of the tonal wedge.

The exposure intervals for each zone are given in the chart. In ascertaining the standard exposure interval for the detail stop, the flash exposure must be considered since without the flash exposure an original terminating in zone twelve would require almost double the detail exposure, yet show no improvement in the result. Therefore, standard for the detail exposure is established at an equivalent necessary to produce an opaque dot from tone eleven of the tonal wedge and the time interval for originals terminating at lighter tones becomes less than standard and for tone twelve greater than standard. As shown in row designated detail interval, tone eleven having a reflection value of twenty and standard exposure interval of one hundred, the method of computing the detail exposure intervals for .copies terminating at either lighter or darker tones'than standard is expressed in the following formula: Reflection value given in column eleven multiplied by exposure interval in detail row and column eleven, divided by new reflection value equals detail exposure interval for new reflection density. The equation thus becomes:

20 times 100 -X In this equation twenty is the reflection density of tone eleven, one hundred the standard exposure interval of tone eleven, N the new reflection density value and X the detail exposure interval for originals terminating at new reflection density. Havingestablished the detail exposure interval, the middletone and highlight exposure intervals are determined by the following equations:

whereas the highlight exposure interval is given in the column of the chart directly agreeing with the lightest tone of the original and the middle- 7 tone exposure interval is ascertained by selecting the exposure interval centrally located between the extremes of the tonal range.

Inasmuch as the highlight and detail zones each embraces five tones it is necessary to establish twenty-five distinct combinations of exposure intervals, which as ascertained by means of the tonal chart have been transferred to a tonal exposure table shown in Fig. 6. This data then provides a convenient means for obtaining the exposure intervals for any required tonal range. i

The exposure table consists of sixv columns, a heading row and twenty-five tonal range rows. Column one is designated Symbol, columns two and three respectively, Highlight and detail extremes, and columns four, five and six, respectively, Detail, highlight and middletone ex- The indicia designating the lightest tone of the highlight zone is located in the second column and the indicia designating the darkest tone of each combination is located in the third column of the tonal exposure table. Each combination is then given a letter which is placed in the first or left hand column and henceforth serves as its symbol. Thus the letter A will indicate a tonal range from one to twelve, whereas the letter T will designate a tonal range from four to eight. The exposure intervals are then recorded in columns four, five ,and six which respectively list the detail, highlight and middletone exposure intervals; Having established the tonal range of the original and noted the required indicia, reference is made to the tonal exposure table. Ascertaining the indicia in the second column which corresponds with the indicla designating the lightest. tone of the original and the indicia in the third column corresponding with the indicia designating the darkest tone of the original, the related symbol from the first column is noted and when necessary the required exposure intervals from columns four, five and six are noted.

The method further includes the establishment of light intensity upon the original to be reproduced. After the original is arranged on the copy-holder I as shown in Fig. 7, the lamps IIH are positioned so as to obtain the greatest practical intensity of light upon the surface'of the original. Due to unavoidable mechanical and physical properties of the lens, a gradual decrease in intensity occurs from the center to the borders of the image which can be compensated for by the proper positioning of the lamps and their reflectors in accordance with the readings resulting. from suitable instrumentalities such as a microamm'eter I02 provided with a graduated dial for indicating in percentages light intensity when electrically connected with a photocell I03 equipped-with an adjustable mask I04 for regulating the admission of light to the photocell. The various areas of the original are scanned by means-of the photocell and the lamps adjusted so that the final reading for all areas of the copy is one hundred on the dial of the microammeter I02 which is considered standard illumination of the original. The photocell is then located adjacent the original so that any fluctuations in the light intensity will be. indicated by the micr'o-.

ammeter and compensated for in the exposure. To establish a standard for light intensity, the lamps should be positioned to yield maximum divided by percent of actual so that this light intensity shall register standard or one hundred on the ammeter. The formulafor establishing variations of light intensity is as follows: Standard light intensity,

light intensity, equals actual light intensity and the equation is:

Whereln U represents standard light intensity, P percentage of standard light intensity and L actual light intensity.

The next step in this method is to select the series of available stops closest in size to' that required as prescribed by the foregoing formulas.

To establish sensitivity of the photographic film, several exposures are made with light intensity. and magnification ratio at unity, employing a standard screen and a standard detail stop. and .varying the interval of time until the counterpart of tone eleven of the tonal wedge is the result of the smallest possible opaque dot in the negative... The correct interval then becomes the.constant in any computation for exposures made with the same batch of sensitive film. The equation for this purpose is ex- .30 pressed as follows:

why

L times J Wherein G represents diameter of standard stop, X detail exposure interval, L actual light intensity, J time variation for required camera extension and V the sensitivity constant.

With all factors directly affecting the screen exposure, subject to control, any deviation from '40 the usual in the extraneous conditions can be 7 more readily recognized and promptly corrected.

The method then consists in correlating the dimensions and effective intervals of the various factors into a definite interval of time for each of the exposures entering into the composite light action on the sensitive film. Having established magnification ratio and camera extension, and ascertained screen separation, screen exposure interval, relevant series of standard stops and inbetween letterfrom the stop chart and tonal range from tone table, the following formulas should be used for calculating the time intervals for the composite exposure:

7 l times 100) detail exposure interval .70 The sensitive film is then exposed through the standard stops and in accordance with the time determined by the previous formulas or as ascertained from stop and exposure table. The exposed film is then developed for a predetermined length of time in a solution kept at a certain degree of temperature, which predetermined time of development is recommended by the manufacturer thereof or the same may be established ,by practice for the particular batch of film or plate.

The foregoing disclosures are offered to an art where at present perfection in the result occurs only by chance. This method offers a comparative simple means for overcoming existing handicaps resulting in part from the human equation element. The problem of computing,- correlating and carrying into execution without scientific aid the combined effects of all factors entering into the composite exposure of a screened negativebeing too complex for the average craftsman to comprehend or perform without error.

What is claimed is:

1. A method of producing screen negatives consisting in ascertaining the screen separation by dividing the square of the width of the screen aperture used by pi times the wave length of light to which the photographic emulsion is predominantly sensitive; ascertaining the diameter of the detail stop opening by dividing by the screen separation the product of the width of the screen aperture and the camera extension; ascertaining the diameter of the highlight stop opening by multiplying by two the diameter of the detail stop opening; ascertaining the diameter of the middletone stop opening by taking the square root of one-half of the sum of the squares of the diameters of the detail and highlight stop openings; ascertaining the tonal range of the original by determining the darkest and lightest tones thereof and comparing the same with an instrumentality having a plurality of tone values varying from the lightest to the darkest tones and determining which of said graduated tones of the instrument correspond with the lightest and darkest tones of the original; ascertaining the reflection density values of the graduated tones which correspond with the tones possessed by the original; and assigning exposure intervals to the several stop openings in accordance with the indicated reflection density values of the tones of said instrumentality which correspond to the lightest and darkest areas of the original and exposing to the original a. photographic emulsion predominantly sensitive to light of a certain wave length, through a ruled screen set at the above-ascertained separation in a camera having such a camera extension and positioned relative to the original that the desired size negative is produced, by means of exposures through detail, middletone and highlight stops having the above-ascertained sizes with the above-assigned exposure intervals, and thereafter developing and fixing the exposed emulsion.

2. A method of producing screen negatives consisting in'ascertaining the screen separation by dividing the square of the width of the screen aperture used by pi times the wave length of light to which the photographic emulsion is predominantly sensitive; ascertaining the diameter of the detail stop opening by dividing by the screen separation the product of the width of the screen aperture and the camera extension; as-

requirements of the tonal range of the original;

and varying the standard intervals for the several tonal zones in accordance with the requirements of the original and exposing to the original a photographic emulsion predominantly sensitive to light of a certain wave length, through a ruled screen set at the above-ascertained separation in a camera having such a camera extension and positioned relative to the original that the desired size negative is produced, by means of exposures through detail, middletone and high light stops having the above-ascertained sizes with the above-modified exposure intervals, and thereafter developing and fixing the exposed emulsion.

3. A method of producing screen negatives consisting in ascertaining the camera extension for reductions by multiplying the focal length of the lens employed by one plus thegiven magnification ratio; ascertaining the screen separation by dividing the square of the aperture of the screen used by pi times the wave length of light to which the photographic emulsion is predominantly sensitive; ascertaining the diameter of the detail stop opening by dividing by the screen separation the product of the width of the aperture of the screen employed and the said camera extension; ascertaining the extent of the outline of the highlight stop opening by multiplying by two the diameter of the detail stop opening; ascertaining the diameter of the middletone stop opening by taking the square root of one-half of the sum of the squares of the diameters of the detail and highlight stop openings; employing a predetermined screen as a standard; ascertaining the tonal range of the original by comparison of the darkest and lightest tones thereof with an instrumentality having a plurality of tone values graduated from maximum to minimum reflection density; determining which of said graduated tones of the instrument coincide with the lightest and darkest tones of the original; ascertaining the reflection density ratio of the tones of the instrumentality which coincide with the lightest and darkest tones possessed by the original; subdividing the tonal range into overlapping zones and assigning said zones respectively to the detail, middletone and highlight stops; ascertaining the required exposure inter-- vals for each zone in accordance with established tonal range; exposing to the original a photographic emulsion predominantly sensitive to light of a certain wave length, through a ruled screen set at the above-ascertained separation in a camera having such a camera extension and positioned relative to the original that the desired size negative is produced, by means of exposures through detail, middletone and highlight stops having the above-ascertained sizes with the above-ascertained exposure intervals, and thereafter developing and fixing the exposed emulsion.

4. A method of producing screened photographic images consisting in ascertaining the required camera extension; ascertaining the screen separation by multiplying the width of the screen aperture by 10 and dividing the product thereof by the pitch of the screen ruling; ascertaining the diameter of the detail stop opening by dividing the product of the width of the screen aperture and the camera extension by the screen separation; ascertaining the diameter of the highlight stop opening by multiplying by two the diameter of the middletone stop opening; ascertaining the diameter of the middletone stop opening by taking the square root of onehalf of the sum ofthe squares of the diameters of the detail and highlight stop openings; ascertaining the tonal range of the original by deter-' mining the darkest and lightest tones thereof and comparing the same with an instrumentality having a plurality of tone values varying from the lightest to the darkest tones and determining which of said tones of the instrumentality correspond with the darkest and lightest tones of the original; ascertaining the reflection density values of the tones of the said instrumentality v i which correspond with the darkest and lightest tones of the original; ascertaining exposure intervals for the several stop openings in accordance with indicated reflection density values; and exposing .to the original a photographic emulsion for the above-ascertained exposure intervals through the ascertained sizes of detail, middletone and highlight stops, and a ruled screenvset at the above-ascertained screen separation in a camera positioned relative to the original and with the required camera extension so that the required size image will result, and thereafter developing and fixing the exposed emulsion.

5. A method of producing screened photographic images consisting in ascertaining the required camera extension; ascertaining the screen separation by multiplying the width of the screen aperture by 10 and dividing the product thereof by the pitch of the screen ruling; ascertaining the diameter of the detail stop opening by dividing theproduct of the width of the screen aperture and the camera extension by the screen separation; ascertaining the diameter of the highlight stop opening by multiplying by two the diameter of the middletone stop opening; ascertaining thediameter of the middletone stop opening by taking the square root of onehalf of the sum of the squares of the diameters of the detail, and highlight stop openings; ascertaining the'tonal range of the original by determining the darkest and lightest tones thereof and comparing the same with an instrumentality having a plurality of tone values varying from the lightest to the darkest tones and determining which of said tones of the instrumentality correspond with the darkest and lightest tones of the original; ascertaining the reflection density values of the tones of the instrumentality which correspond with the darkest and lightest tones of the original; ascertaining exposure intervals for the several stop openings in accordance with indicated reflection density values; checking the illumination of the original for light intensity; adjusting the source of illumination so as to obtain the maximum practical intensity on all portions of the original; and exposing to the original illuminated with the aforesaid maximum practical intensity a photographic emulsion for the above-ascertained exposure intervals through the-ascertained sizes of detail, middletone and highlight stops, and a ruled screen set at the above-ascertained screen separation in a camera positioned relative to the original and with the required camera extension so that the required size image will result, and thereafter developing and fixing the exposed emulsion.

6. A method of producing screened photographic images consisting in ascertaining the required camera extension; ascertaining the screen separation by multiplying the width of the screen aperture by 10 and dividing the product thereof by the pitch of the screen ruling;- asoertaining the diameter of the detail stop opening by dividing the product of the width of the screen aperture and. the camera extension by the screen separation; ascertaining the diameter of the highlight'stop opening by multiplying by two the diameter of the middletone stop opening; ascertaining the diameter of the middletone stop opening by taking the square root of one-half of the sum of the squares of the diameters of the detail and highlight stop openings; ascertaining the tonal range of the original by determining the darkest and lightest tones thereof and comparing the same with an instrumentality having a plurality 'of tone values varying from the lightest to the darkest tones and determining which of said tones of the instrumentality correspond with the darkest and lightest tones of the original; ascertaining the reflection density values of the tones of the instrumentality which correspond with the darkest and lightest tones of the original; ascertaining exposure intervals for the several stop openings in accordance with indicated reflection density values; varying the ascertained exposure intervals proportionate to the sizes of the said ascertained stop openings with reference to available sizes of stop openings; and exposing to the original a photographic emulsion for the above-modified exposure intervals through said available sizes of detail, middletone and highlight stops, and a ruled screen set at the above-ascertained screen separation in a camera positioned relative to the original and with the required camera extension so that the required size image will result, and thereafter developing and fixing the exposed emulsion.

7. A method of producing screened photographic images consisting in ascertaining the required camera extension; ascertaining the screen separation by multiplying the width of the screen aperture by 10% and dividing the product thereof by the pitch of the screen ruling; ascertaining the diameter of the detail stop opening by dividing the product of thewidth of the screen aperture and the camera extension by the screen separation; ascertaining the diameter of the highlight stop opening by multiplying by two the diameter of the middletone stop opening; ascertaining the diameter of the middletone stop opening by taking the square root of onehalf of the sum of the squares of the diameters of the detail and highlight stop openings; ascertaining the tonal range of the original by determining the darkest and lightest tones thereof and comparing the same with an instrumentality having a plurality of tone values varying from the lightest to the darkest tones and determining which of said tones of the instrumentality correspond with the darkest and lightest tones of the original; ascertaining the reflection density values of the tones of the instrumentality ance with the indicated reflection density values; checking the illumination of the original for light intensity; adjusting the source of illumination so as to obtain the maximum practical intensity on all portions of the original; varying the ascertained exposure intervals proportionate to the sizes of the said ascertained stop openings with reference to available sizes of stop openings and exposing to the original illuminated with the aforesaid maximum practical intensity a photographic emulsion for the above-modified exposure intervals through said available sizes of detail, middletone and highlight stops, and a ruled screenv set at the above-ascertained screen separation in a camera positioned relative to the original and with the required camera extension so that the required size image will result, and thereafter developing and fixing the exposed emulsion.

8. In the art of screen photography, a method of determining exposure values for ,thedetail, highlight and middletone zones of an original which includes the use of detail, highlight and middletone lens stop openings, the middletone lens stop opening for predominantly recording the tonal values of the middletone zone being twice the size of the detail stop opening employed for predominantly recording the tonal values of the detail zone and-one-half the size of the highlight stop opening employed for predominantly recording the tonal values of the highlight zone; ascertaining the tonal range of the original by selecting the darkest and lightest tones thereof and comparing the said tones with an instrumentality having a plurality of tones graduated from the darkest to the lightest tones to determine which of said tones of the instrumentality correspond with the darkest and lightest tones of the original; assigning graduated reflection density values to the several tones of the instrumentality; ascertaining exposure values for each of the tones of the instrumentality proportionate to the assigned reflection density values; ascertaining the reflection density values of the tones of said instrumentality which correspond with the darkest and lightest tones of the original and from these reflection density values and the respective sizes of the detail and highlight stop openings ascertaining the exposure values for the detail and highlight zones of the original; ascertaining the reflection density value of the tone of said instrumentality located centrally between the tones of said instrumentality which correspond with the darkest and lightest tones of the original and from said reflection density value and the size of the middletone stop opening ascertaining the exposure value for the middletone zone; then utilizing these exposure values in arriving at exposure intervals for said zones and exposing a light sensitive emulsion to the said original for the several intervals of time through the respective stop openings.

' AUGUST C. HANSCH.

HENRY E. HANSCH. 

